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This thesis investigates an alternative solution to deal with the civil structure vibration. Non-contact electromagnetic or Eddy current damping is selected as a score of vibration suppression. Electromagnetic damping relies on the interaction between a permanent magnet and conductor. An electromagnetic damper (EMD) is applied both to a laboratory footbridge structure and 6-storey model-scale aluminium moment resisting frame (AMRF). In this first study the EMD is connected in series with an electronic shunt circuit to construct an electromagnetic shunt damper (EMSD). A robust optimisation method is applied to develop the corresponding optimal design formula of the EMSD. The principle of an EMSD is to convert mechanical energy to electrical energy. Hence, the induced electromotive force (emf) is generated by electromagnetic induction. This emf induces an amount of shunt damping, which is fedback to the structure to achieve vibration suppression. It was found that when the impedance was applied, the shunt damping feature was of a similar nature to viscous dampers. In contrast, when an RLC (resistance-inductance-capacitance) circuit is connected, the shunt damping is analogous to a tuned mass damper. A second form of EMD is Eddy current damper (ECD), which relies on a geometrical arrangement of permanent magnets and conductors to produce damping forces. The vertical and horizontal orientation of the magnet, unidirectional and alternative pole projection and moving different direction of the conductor are investigated. A theoretical study involving the infinite boundary and finite boundary (the method of images current) is carried out to obtain an analytical calculation of the damping force. On the basis of this analysis, one type of ECD prototype was physically built. A performance test was carried out to determine the damping characteristics of the ECD, which agreed with the results of the numerical analysis. In addition, the ECD was applied to control the dynamics of the 6-storey AMRF. It was found that, the ECD can effectively increase system damping and have a satisfactory control effect.

Reliable flutter analysis of aircraft structures is a major requirement to determine safe flight envelops. Dynamically equivalent finite element model of an aircraft structure correlating well with experimental modal is a major requirement for a reliable flutter analysis. Currently available model updating techniques require enormous time and engineering work to achieve appropriate finite element models of aircraft structures. The method developed within the scope of this thesis work aims to remove important disadvantages of common model updating procedures. In doing this, the method starts with a simple finite element mesh obtained by connecting measurement points, used in the Ground Vibration Test of an aircraft structure, with 3 D Euler-Bernoulli beam elements. Initial estimates of the geometric and material properties are determined by solving structural identification equations derived from the mass and stiffness orthogonality of experimental modes. By using those initial estimates, an initial finite element model is constructed. Starting from this initial finite element model, structural identification equations are updated and solved iteratively by using experimental natural frequencies and eigenvectors of the v updated finite element model representing the same mode shapes with measured normal modes. Iterations are continued until eigen solution of the updated finite element model closely correlates with experimental modal data. The applicability of the method is illustrated on a scaled aircraft model and a real aircraft structure. The results are quite satisfactory but the method requires further improvements to achieve a much better correlation level in case of real aircraft structures.

L’amélioration du caractère prédictif des simulations numériques requiert une meilleure maîtrise des modèles constitutifs. Des procédures d’identification exploitant des mesures de champs ont été développées afin de valider les modèles et d’identifier un jeu de paramètres constitutifs à partir d’un nombre réduit d’essais hétérogènes. Bien évidemment, les résultats de telles procédures dépendent grandement des incertitudes des mesures. Dans cette thèse, une stratégie d’identification de paramètres constitutifs à partir de mesures de champs par corrélation d’images numériques éléments finis (CIN-EF) multi-échelles est proposée et développée. Une variante régularisée du recalage par éléments finis (FEMU-R) est adaptée à cette approche multi-échelles. Elle exploite des champs de déplacements mesurés par CIN-EF d'une part à l’échelle de la structure (fournissant les conditions aux limites pour la simulation EF) et d’autre part à une échelle plus locale (fournissant des champs de déplacements mieux résolus pour la comparaison essais/calculs). Un algorithme de recalage d’images est développé pour faire le lien entre les échelles. D’abord validée à l’aide d’images de synthèse, la procédure est ensuite appliquée à un essai de traction sur plaque trouée réalisé sur un composite stratifié verre/époxy. On montre qu’une telle stratégie permet de diminuer nettement non seulement les incertitudes de mesure mais également les incertitudes d’identification. Finalement, la question d’un mouchetis adapté à cette approche multi-échelles est évoquée et des éléments de solutions sont proposés et testés. / Improving the prediction of numerical simulations requires a better control of constitutive models. Identification methods exploiting full-field measurements have been developed in order to validate models and to identify a set of constitutive parameters from a reduced number of heterogeneous tests. The results of those methods largely depends on measurement uncertainties. In this PhD thesis, a strategy is proposed and developed for the identification of constitutive parameters from full-field measurements obtained by multiscale finite element digital image correlation (FE-DIC). A Regularised Finite Element Model Updating method (FEMU-R) is adapted to this multiscale approach. It exploits displacement fields measured by FE-DIC at a structural scale (in order to obtain the boundary conditions for FE simulation)and at a local scale (giving a better resolution on the displacement field for the comparison between experiment and simulation). An image registration algorithm is developed to bridge these scales. First validated on synthetic images, the multiscale approach is then applied to an open-hole tensile test of a glass/epoxy composite laminate. It is shown that such a strategy allows to reduce not only the measurement uncertainties but also the identification uncertainties. Finally the question of a speckle pattern suitable for this approach is discussed and some first technical solutions are proposed and tested.

Submitted by SIDNEY BRUCE SHIKI null (sbshiki@gmail.com) on 2016-04-02T14:43:01Z No. of bitstreams: 1 Thesis_PhD_SBShiki.pdf: 10090180 bytes, checksum: c44d2ebecbed6d011cf61ceabdfd3494 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-04-05T14:42:00Z (GMT) No. of bitstreams: 1 shiki_sd_dr_ilha.pdf: 10090180 bytes, checksum: c44d2ebecbed6d011cf61ceabdfd3494 (MD5) / Made available in DSpace on 2016-04-05T14:42:00Z (GMT). No. of bitstreams: 1 shiki_sd_dr_ilha.pdf: 10090180 bytes, checksum: c44d2ebecbed6d011cf61ceabdfd3494 (MD5) Previous issue date: 2016-03-04 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Estruturas com comportamento não-linear são frequentes em dinâmica estrutural, principalmente considerando componentes parafusados, com juntas, folgas ou estruturas flexíveis sujeitas à grandes deslocamentos. Desse modo, o monitoramento de estruturas com métodos lineares clássicos, como os baseados em parâmetros modais, podem falhar drasticamente em caracterizar efeitos não-lineares. Neste trabalho foi proposta a utilização de séries de Volterra para identificação de sistemas mecânicos não-lineares em aplicações de detecção de danos e quantificação de parâmetros. A propriedade deste modelo de representar separadamente os componentes de resposta linear e não-linear do sistema foi aplicada para se construir índices de dano que evidenciam a necessidade de modelagem não-linear. Além disso métricas de resíduo linear e não-linear dos termos do modelo de Volterra são empregadas para identificar modelos paramétricos da estrutura. As metodologias propostas são ilustradas em bancadas experimentais de modo a evidenciar a importância de fenômenos não-lineares para o monitoramento de estruturas. / Nonlinear structures are frequent in structural dynamics, specially considering screwed components, with joints, clearance or flexible components presenting large displacements. In this sense the monitoring of systems based on classical linear methods, as the ones based on modal parameters, can drastically fail to characterize nonlinear effects. This thesis proposed the use of Volterra series for nonlinear system identification aiming applications in damage detection and parameter quantification. The property of this model of representing the linear and nonlinear components of the response of a system was used to formulate damage features to make clear the need of nonlinear modeling. Also metrics based on the linear and nonlinear residues of the terms of the Volterra model were employed to identify parametric models of the structure. The proposed methodologies are illustrated in experimental setups to show the relevance of nonlinear phenomena in the structural health monitoring. / FAPESP: 2012/04757-6 / FAPESP: 2013/25148-0 / FAPESP: 2012/21195-1 / FAPESP: 2015/03560-2

Orientador: Samuel da Silva / Abstract: Nonlinear structures are frequent in structural dynamics, specially considering screwed components, with joints, clearance or flexible components presenting large displacements. In this sense the monitoring of systems based on classical linear methods, as the ones based on modal parameters, can drastically fail to characterize nonlinear effects. This thesis proposed the use of Volterra series for nonlinear system identification aiming applications in damage detection and parameter quantification. The property of this model of representing the linear and nonlinear components of the response of a system was used to formulate damage features to make clear the need of nonlinear modeling. Also metrics based on the linear and nonlinear residues of the terms of the Volterra model were employed to identify parametric models of the structure. The proposed methodologies are illustrated in experimental setups to show the relevance of nonlinear phenomena in the structural health monitoring. / Resumo: Estruturas com comportamento não-linear são frequentes em dinâmica estrutural, principalmente considerando componentes parafusados, com juntas, folgas ou estruturas flexíveis sujeitas à grandes deslocamentos. Desse modo, o monitoramento de estruturas com métodos lineares clássicos, como os baseados em parâmetros modais, podem falhar drasticamente em caracterizar efeitos não-lineares. Neste trabalho foi proposta a utilização de séries de Volterra para identificação de sistemas mecânicos não-lineares em aplicações de detecção de danos e quantificação de parâmetros. A propriedade deste modelo de representar separadamente os componentes de resposta linear e não-linear do sistema foi aplicada para se construir índices de dano que evidenciam a necessidade de modelagem não-linear. Além disso métricas de resíduo linear e não-linear dos termos do modelo de Volterra são empregadas para identificar modelos paramétricos da estrutura. As metodologias propostas são ilustradas em bancadas experimentais de modo a evidenciar a importância de fenômenos não-lineares para o monitoramento de estruturas. / Doutor

No description available.

In the year 2006, only 10 years after the steel- concrete composite bridge, Vårby bridge was built, fatigue cracks were found during an inspection. To further investigate the reasons and the potential danger of the cracks, an investigation under the commission of the Swedish Transport Administration was issued in 2009. After the detection of fatigue cracks, several measurements were carried out in order to monitor the static behavior by the use of strain gauges at selected positions along the bridge. The measurements from the strain gauges monitoring the global behavior were then used to calibrate an finite element model.   The present report is part of the research of understanding the behavior of steel-concrete composite bridges. Numerical analysis and model updating have been used in order to understand and determine how different parameters affects the strain range and the global behavior. The numerical analysis and parameter study were performed in the Finite Element software Abaqus and programming language Python. The outcome of the parameter study was then used to perform the model updating by the method of falsification in MATLAB.   The results from the parameter study and the model updating showed that the measured strains could be reached with a wide range of parameter combinations. Even with unreasonable parameter values, the measured strains were obtained. To investigate the reason for this, a multiple linear regression analysis was performed which showed that the strain range is strongly correlated to the Young’s modulus of steel and concrete and also to the connector elasticity, which resembles the studs in the real bridge.   Two different finite element models, with two completely different input parameter values, obtain the same strain range for the global behavior. It is therefore not certain to assume that a model is accurate and valid based on the fact that the predicted strain range from the finite element model is close to the measured strain range since the global behavior of a steel- concrete composite bridge can be modeled by many different sets of parameters.

Ce travail se place dans le cadre de l'assimilation de données en mécanique des structures. Il vise à développer de nouveaux outils numériques pour l'assimilation de données robuste et en temps réel afin d'être utilisés dans diverses activités d'ingénierie. Une activité cible est la mise en œuvre d'applications DDDAS (Dynamic Data Driven Application System) dans lesquelles un échange continu entre les outils de simulation et les mesures expérimentales est requis dans le but de créer une boucle de contrôle rétroactive sur des systèmes mécaniques connectés. Dans ce contexte, et afin de prendre en compte les différentes sources d'incertitude (erreur de modélisation, bruit de mesure,...), une méthodologie stochastique puissante est considérée dans le cadre général de l’inférence bayésienne. Cependant, un inconvénient bien connu d'une telle approche est la complexité informatique qu’elle engendre et qui rend les simulations en temps réel et l'assimilation séquentielle des données difficiles.Le travail de thèse propose donc de coupler l'inférence bayésienne avec des techniques numériques attrayantes et avancées afin d'envisager l’assimilation stochastique de données de façon séquentielle et en temps réel. Premièrement, la réduction de modèle PGD est introduite pour faciliter le calcul de la fonction de vraisemblance, la propagation des incertitudes dans des modèles complexes et l'échantillonnage de la densité a posteriori. Ensuite, l'échantillonnage par la méthode des Transport Maps est étudiée comme un substitut aux procédures classiques MCMC pour l'échantillonnage de la densité a posteriori. Il est démontré que cette technique conduit à des calculs déterministes, avec des critères de convergence clairs, et qu'elle est particulièrement adaptée à l'assimilation séquentielle de données. Là encore, l'utilisation de la réduction de modèle PGD facilite grandement le processus en utilisant les informations des gradients et hessiens d'une manière simple. Enfin, et pour accroître la robustesse, la correction à la volée du biais du modèle est abordée à l'aide de termes d'enrichissement fondés sur les données. Aussi, la sélection des données les plus pertinentes pour l’objectif d’assimilation est abordée.Cette méthodologie globale est appliquée et illustrée sur plusieurs applications académiques et réelles, comprenant par exemple le recalage en temps réel de modèles pour le contrôle des procédés de soudage, ou l’étude d'essais mécaniques impliquant des structures endommageables en béton instrumentées par mesures de champs. / The work is placed into the framework of data assimilation in structural mechanics. It aims at developing new numerical tools in order to permit real-time and robust data assimilation that could then be used in various engineering activities. A specific targeted activity is the implementation of DDDAS (Dynamic Data Driven Application System) applications in which a continuous exchange between simulation tools and experimental measurements is envisioned to the end of creating retroactive control loops on mechanical systems. In this context, and in order to take various uncertainty sources (modeling error, measurement noise,..) into account, a powerful and general stochastic methodology with Bayesian inference is considered. However, a well-known drawback of such an approach is the computational complexity which makes real-time simulations and sequential assimilation some difficult tasks.The PhD work thus proposes to couple Bayesian inference with attractive and advanced numerical techniques so that real-time and sequential assimilation can be envisioned. First, PGD model reduction is introduced to facilitate the computation of the likelihood function, uncertainty propagation through complex models, and the sampling of the posterior density. Then, Transport Map sampling is investigated as a substitute to classical MCMC procedures for posterior sampling. It is shown that this technique leads to deterministic computations, with clear convergence criteria, and that it is particularly suited to sequential data assimilation. Here again, the use of PGD model reduction highly facilitates the process by recovering gradient and Hessian information in a straightforward manner. Eventually, and to increase robustness, on-the-fly correction of model bias is addressed using data-based enrichment terms.The overall cost-effective methodology is applied and illustrated on several academic and real-life test cases, including for instance the real-time updating of models for the control of welding processes, or that of mechanical tests involving damageable concrete structures with full-field measurements.

This master thesis covers the dynamic soil structure interaction of soil-steel culverts applyinga methodology based on the frequency domain response. At the first stage of this masterthesis, field tests were performed on one bridge using controlled excitation. Then, themethodology followed uses previous research, the field tests, finite element models (FEM)and perfectly matched layer (PML) elements.Firstly, a 2D model of the analysed bridge, Hårestorp, was made to compare the frequencyresponse functions (FRF) with the ones obtained from the field tests. Simultaneously, a 3Dmodel of the bridge is created for the following purposes: compare it against the 2D modeland the field tests, and to implement a model updating procedure with the particle swarmalgorithm to calibrate the model parameters. Both models use PML elements, which areverified against previous solution from the literature. The verification concludes that thePML behave correctly except for extreme parameter values.In the course of this master thesis, relatively advanced computation techniques were requiredto ensure the computational feasibility of the problem with the resources available.To do that, a literature review of theoretical aspects of parallel computing was performed, aswell as the practical aspects in Comsol. Then, in collaboration with Comsol Support and thehelp given by PDC at KTH it was possible to reduce the computational time to a feasiblepoint of around two weeks for the model updating of the 3D model.The results are inconclusive, in terms of searching for a perfectly fitting model. Therefore,further research is required to adequately face the problem. Nevertheless, there are some accelerometerswhich show a considerable level of agreement. This thesis concludes to discardthe 2D models due to their incapability of facing the reality correctly, and establishes a modeloptimisation methodology using Comsol in connection with Matlab.